To date, a great variety of rapid fire sub-machine guns or rapid fire pistols are known, which generally function by means of a mechanism known as an open cover inasmuch as these are low pressure arms. These arms always include a case inside of which the firing and safety mechanism are located, as well as the firearm bolt, and to which case the grip of the firearm is joined, together with or separately from the magazine of the same, the barrel and, optionally, a detachable or folding stock.
These known sub-machine guns have many disadvantages; thus when the stock is needed, since the barrel is joined to the case, these firearms turn out to be of considerable length, and therefore very cumbersome. In order to avoid the above, folding stocks were thought of; nevertheless, these also have disadvantages because after firing or when needed to strike with, they are not very adequate inasmuch as they bend since they are not fixed.
Another disadvantage of the folding stock is that in the case of combat fractions of a minute are very important, and getting the stock in place slows down the operation.
One of the greatest problems and disadvantages of the known sub-machine guns is that when the bolt is included within the case it can always jam due to foreign matter getting into the case; this is very dangerous because when it is not possible to move the bolt in time to free the firing mechanism of the firearm, or it moves in an inadequate manner, the desired shot will not be produced or said shot will be interfered with and thus dangerous to the shooter.
Aside from the aforementioned disadvantages, another difficulty with having the bolt inside the case is that the cleaning of the same is complicated and requires appreciable time, time that must be taken into consideration for, as has already been said, in the case of combat, it is all important.
An additional problem with the interior bolt is that it requires guides which guide it in its travel and, also, it includes only a simple dwell or retention lever on the same.
Another of the problems of the known sub-machine guns is that the type of safety used is generally related to the trigger or firing device, which in reality does not provide for complete reliability inasmuch as on many occasions it allows the arm to fire without squeezing the trigger; and this causes innumerable accidents since there is no set target. Also we can not really be certain that the firearm is not ready to fire. And there is no assurance against this because if the firearm were for example to be dropped and strike on the back side it would actually fire as the bolt moved as a result of the shock of the fall; and consequently said accidents can occur.
Another disadvantage of this type of known firearms is that in all of them, after they have been used for some time, the firing pin or device that causes the detonation of the primer of the cartridges deteriorates and does not function properly and therefore must be replaced by a new one.
Finally, another problem with the known sub-machine guns is that the sight included in the chamber is fixed and in many cases there is no way to adjust it according to the conditions of firing the firearm. Consequently these arms do not afford very accurate aim, and in firearms this is definitely necessary.